Pulse oximeters

Pulse oximeters use red and infra-red light to monitor pulse rate and the oxygenation of a patient’s blood.

The body scatters and absorbs visible and near infra-red wavelengths significantly so that in order to have a measurable signal thin parts of the body must be used.

A typical pulse oximeter consists of light emitting diodes (LEDs) mounted opposite light sensors in a clip that can be attached across a finger or earlobe.

As the light produced by the LEDs travels through the body it is absorbed by an amount that is dependent on its wavelength and the average number of oxygen atoms attached to each haemoglobin molecule.

The amount absorbed also fluctuates as the arteries expand and contract in response to each heart beat allowing the pulse oximeter to determine the pulse rate as well as blood oxygen saturation from the transmitted signal.